LET’S TAKE A LOOK AT WHAT ALL OF THESE SITE COLLECTIONS IN SHAREPOINT ARE
This is the default site collection for you to create your Intranet in. That is the place to create new team sites, department sites, document management sites. You don’t need to use this particular site collection for Intranet, and can always create a new one (more on this later in the post), but this one has the cleanest (shortest) URL that is easy to remember!
The second site collection in the list is /portals/hub. This is a site collection that contains all the videos you would post to the Office 365 Video Portal. I have written a detailed post on Video Portal – check it out. Office 365 Video Portal is like an internal YouTube for your organization. You can post all sorts of videos, and organize them by channels, just like on YouTube. It can be real handy for the training, marketing, and other company videos.
You might or might not see this site collection in the list. In case you do, this site collection is a dedicated space with the Community features enabled. It allows Administrators to manage discussions in a virtual environment. I honestly do not see this feature used by many organizations, so I would not sweat over it if I were you. Just know what this site collection is in case you see it, and let’s move on! If you have spare time on your hands, you can read more about this site collection here (official Microsoft article).
This is the site collection that is responsible for searches in your SharePoint environment. Anytime you search your SharePoint (i.e., using the search box in the upper right-hand corner of the SharePoint site), this site collection (officially known as the Search Center) processes the queries and displays results to the users. If you ever wanted to adjust how your search results are displayed or how search query/logic works, you would be modifying the Search Center (this particular site collection). You can also create additional search centers (site collections) to provide users with alternate search experience, but that is the topic for some future blog post.
For more information refer this link,